When are the monsoon expected in Kolkata, India this year?

1st week June.But it could be earlier than normal expected.

Offcial Monsoon date for Calcutta is 8th June

NO MONSOON THIS YEAR.

last week of May to 1st week of June.

The main monsoon season in India runs from June to September and the question on everyone’s lips is always, “What's it really like and is travel still possible?” This is very understandable as the thought of rain and floods is enough put a dampener any holiday. However, the good news is that you don’t have to let the monsoon ruin your travel plans, and travel can even be advantageous during this time. The southwest summer monsoon is attracted to India by a low pressure area that's caused by the extreme heat of the Thar Desert and adjoining areas, during summer. Moisture-laden winds from the Indian Ocean come to fill up the void, but because they can't pass through the Himalaya region, they're forced to rise. The gain in altitude of the clouds results in a drop in temperature, bringing about rain. When the southwest monsoon reaches India, it splits into two parts around the mountainous region of the Western Ghats in south-central India. One part moves northwards over the Arabian Sea and up the coastal side of the Western Ghats. The other flows over the Bay of Bengal, up through Assam, and hits the Eastern Himalaya range. It’s important to note that some regions receive more rain than others during the monsoon. Out of India's major cities, Mumbai receives the most rain, followed by Kolkata (Calcutta). The eastern Himalaya region, around Darjeeling and Shillong, is one of the wettest areas in not just India, but the whole world, during the monsoon. This is because the monsoon picks up additional moisture from the Bay of Bengal as it heads towards the Himalaya range. Travel to this region should definitely be avoided during monsoon time.